Prostaglandin derivative of the above formula (1) is known in Drugs of the Future, 1992, 17(8), 691-704; J. Med. Chem., 1993, 36, 243-248, etc. and a process of the following Reaction Scheme 1 published in WO 93/00329 can be mentioned as the typical synthesis thereof. 
In the above process, ω-chain is introduced into the starting material of Corey lactone by Wadworth-Emmons method, the ketone group at C15 position is reduced to an alcohol group, the remained double bond is reduced again using Pd, α-chain is introduced into a lactol as obtained through some consecutive reactions by Wittig reaction, and the terminal group is esterified.
However, the above process has been identified to have the following problems.
First, the diastereomeric mixture resulted from the introduction of ω-chain and reduction of the ketone group at C15 position comprises 15S-isomer and 15R-isomer in a ratio of 7:3. Therefore, stereoselectivity of the process is not satisfactory. Further, since these isomers can hardly be separated, the yield of the desired 15S-isomer is as very low as 38%.
Second, the yield of the esterification reaction of the terminal carboxylic acid after introduction of α-chain by Wittig reaction is reported to be less than 40%. This is the final step of the process, and so the low yield of the final step reaction may exert fatal and serious influence on the total efficacy of the synthesis.
Third, Corey lactone used as a starting material is very expensive, which makes the total process uneconomic.